Reduced-emissions combustion utilizing multiple-component metallic combustion catalyst

Abstract

Residual fuels, as well as lighter distillate fuels, are combusted with greater efficiency by utilizing low concentrations of specific bimetallic or trimetallic fuel-borne catalysts. The catalysts reduce fouling of heat transfer surfaces by unburned carbon while limiting the amount of secondary additive ash which may itself cause overloading of particulate collector devices or emissions of toxic ultra fine particles when used in forms and quantities typically employed. By utilizing a fuel containing a fuel-soluble catalyst comprised of platinum and at least one additional metal comprising cerium and / or iron, production of pollutants of the type generated by incomplete combustion is reduced. Ultra low levels of nontoxic metal combustion catalysts are able to be employed for improved heat recovery and lower emissions of regulated pollutants.

Description

[0001]This application claims the benefit of Provisional Application No. 60 / 354,435, filed Feb. 4, 2002.BACKGROUND OF THE INVENTION[0002]The invention concerns new compositions and a new process for improving the efficiency of fossil fuel combustion sources, especially lean-NOx combustors, by reducing the fouling of heat transfer surfaces by unburned carbon while limiting the amount of secondary additive ash. Utilizing a fuel containing a fuel-soluble catalyst comprised of platinum and at least one additional metal also reduces production of pollutants of the type generated by incomplete combustion, e.g., particulates, unburned hydrocarbons and carbon monoxide.[0003]Efforts to improve power generation efficiency have often lead to the use of heat recovery steam generators to obtain additional flue gas heat recovery. This has the advantage of improving cycle efficiency, but unburned carbon can form deposits and reduce heat transfer in these devices. Moreover, the use of combustion ca...

AI Technical Summary

Benefits of technology

[0008]The invention provides a new process addressing the above needs of combustors such as turbines, boilers, furnaces, process heaters, heat recovery units, diesel engines, and the like, utilizing carbonaceous, e.g., fossil fuels such as distillates, residual and gaseous fuels. It is an advantage of the invention that improvements can be achieved without the use of after treatment devices, such as filters or catalysts, e.g., diesel particulate filters (DPF's) or diesel oxidation catalysts (DOC's) in the case of diesel engines.

[0009]The fuel employed according to the invention comprises carbonaceous fuel, e.g., fossil fuel, containing low or ultra low levels of catalyst metal additives. The catalyst metal additives will preferably be soluble or dispersible in the fuel and contain platinum and cerium and / or iron compositions, but in some cases can be added in whole or in part to the combustion air.

[0010]In one aspect, the process will comprise: mixing with fuel or combustion air a multi-component combustion catalyst comprising a platinum composition and cerium and / or iron compositions at levels reduced to as low as 0.0005 ppm for platinum and levels as low as 0.5 ppm for the cerium and iron; and combusting fuel with air in the presence of the catalyst in a regimen of treatment that will utilize effective catalyst levels for a time and under conditions, which will achieve one or more of the noted improvements. In one aspect, low catalyst levels can be employed for at least a portion of a treatment regimen, which can also include employing a higher initial dose and / or intermittently using higher catalyst levels. The ratio of cerium and / or iron to platinum will be within the range of from 3:1 to 100,000:1, but more typically will be in the range of from 100:1 to 20,000:1. Cerium is a preferred catalyst metal when the fuel is No. 2 fuel oil, and a combination of cerium and iron are preferred when the fuel is a residual oil, such as No. 6 oil.

[0011]The invention has particular advantage in improving combustion in processes such as the burning of fuels which are notoriously dirty in terms of soot generation, typically heavy fuels, e.g., residual fuels like No. 4, 5 and 6 oils. These oils are characterized by high viscosities, being just barely pourable or unpourable at 70° F., contain high levels of condensed aromatics and tend to be difficult to combust fully and cleanly. In this case, the multi-component catalyst can be employed as a combustion aid to reduce soot formation initially and / or to aid auto combustion of soot in the ductwork downstream of the combustor. Typical of low catalyst levels for at least a part of a treatment regimen are platinum concentrations of from only 0.0005 to less than 0.15, e.g., less than 0.1, ppm and cerium and / or iron at total concentrations of from only 0.5 to less than 20, e.g., less than about 15, ppm. In some embodiments, the treatment regimen can call for the utilizing higher catalyst concentrations initially or at defined intervals or as needed—but not for the whole treatment as has been necessary in the past. In some cases, platinum concentrations can be as high as 1 ppm or even up to 2 ppm, as needed.

[0012]The invention has similar advantage in the case of burning lighter fuels, such as those categorized as fuel oils, such as No. 2 fuel oil, which can result in lesser, but significant production of carbonaceous soot. Typical of low catalyst levels for at least a part of a treatment regimen are platinum concentrations of from only 0.0005 to less than 0.15, e.g., less than 0.1, ppm and cerium and / or iron at total concentrations of from only 0.05 to less than 8 ppm. Again, in some embodiments, the treatment regimen can call for the utilizing higher catalyst concentrations initially or at defined intervals or as needed. For No. 2 fuel oil, a bimetallic FBC containing platinum and cerium is preferred.

[0013]The invention also has significant beneficial use in the area of dual-fuel diesel engines, which although they operate principally on natural gas, utilize a more smoke-producing pilot fuel such as regular diesel fuel. In some cases the catalyst concentrations according to the invention can be the above-noted low catalyst levels for at least a part of a treatment regimen, with platinum concentrations of from only 0.0005 to less than 0.15 ppm, e.g., less than 0.1 ppm, say 0.01 to 0.09 ppm, and cerium and / or iron at total concentrations of from only 0.5 to less than 8 ppm. In some cases, it will be useful to utilize less than 0.05 ppm platinum and a total catalyst level of less than 5 ppm.

Problems solved by technology

These oils are characterized by high viscosities, being just barely pourable or unpourable at 70° F., contain high levels of condensed aromatics and tend to be difficult to combust fully and cleanly.

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